1. Field of the Invention
This invention relates generally to optical communication networks. More particularly, this invention relates to optical communication networks having a primary optical transmission path and a secondary or protection optical transmission path between nodes of the network. Even more particularly, this invention relates to apparatus and methods for detecting a fault within the primary optical transmission path and automatically transferring optical signals being conveyed on the primary optical transmission path to the secondary or protection optical transmission path.
2. Description of Related Art
In optical communication networks, reliability of the network is increased by placing an active or primary optical transmission path or cable and a secondary redundant or protection optical transmission path or cable from a transmission node to a reception node. In such networks as Synchronous Optical Networking (SONET), the nodes are distributed and connected in a ring fashion. The primary ring carries the optical signals with a secondary ring being routed between the nodes of the network to provide the necessary redundancy. If a link within a ring of the primary ring has a fault, the node detects the fault and re-routes the traffic on the ring to the secondary ring, such that the fault in the primary ring is by-passed and the network remains operational.
Other networks simply provide the primary and secondary optical transmission path between two nodes. The optical signals are conveyed on the primary optical transmission path during normal operation and if a fault occurs on the primary optical transmission path, the optical signals are routed to the secondary or protection optical transmission paths. The optical signals are detected, recovered, and decoded to determine whether a fault has occurred. A multiplexer is used to change the selection of the primary optical transmission path to the protection optical transmission path when a fault is detected. By having the fault detection occur in the receiving node electronic, time elapses and the communicated messages within the optical signals maybe lost or require extensive resending diminishing the performance of the network.
“Channel Protection in WDM Mesh Networks”, Gadiraju, et al., IEEE Workshop on High Performance Switching and Routing, 2001, IEEE, pp. 26-30, focuses on a channel protection technique against single failures within reliable optical link networks with or without wavelength converters. The protection technique is introduced based on the 1:N spare capacity assignment and has been incorporated in routing and wavelength assignment and network cost optimization. The method involves changing the protection wavelength after each failure.
“Generalized Loop-Back Recovery In Optical Mesh Networks”, Medard, et al., IEEE/ACM Transactions on Networking, Volume: 10, Issue: 1, February 2002, IEEE, pp. 153-164 details a novel scheme for performing loop-back in optical mesh networks. Algorithms are detailed that perform recovery for link failure and generalized loop-back recovery for node failure.
“On Available Bandwidth In FDDI-Based Reconfigurable Networks”, Kamat, et al., Proceedings IEEE 13th INFOCOM '94—Networking for Global Communications, June, 1994, vol. 3, pp. 1390-1397 details an FDDI-based reconfigurable network (FBRN) that can survive multiple faults. An FBRN consists of multiple FDDI trunk rings and has the ability to reconfigure itself in the face of extensive damage.
“Optimal Spare Capacity Design For Various Protection Switching Methods In ATM Networks”, Frisanco, et al., IEEE International Conference on Communications (ICC 97 Montreal)—‘Towards the Knowledge Millennium’, 1997, vol. 1, pp. 293-298 describes various protection switching methods for ATM networks and presents mathematical models that can be used to determine globally optimal restoration paths and to define spare capacities in the network.
U.S. Pat. No. 5,327,275 (Yamane, et al.) illustrates a switching system for optical communication between first and second optical terminal stations. Optical transmission lines connect first and second optical terminals to their respective working optical transmission lines. A protection piece of optical terminal equipment is connected to the protection optical transmission line. Bidirectional optical signal paths are provided to the corresponding working pieces of optical terminal equipment.
U.S. Pat. No. 5,442,623 (Wu) teaches a method of operation for a self-healing, passive protected ring network. The ring network includes a plurality of active nodes. To make a working ring, these nodes are interconnected. In order to correct a possible failure in the optical fibers or nodes of the working ring, the optical switches are set to connect the protection ring to the nodes on either side and to bypass all the other nodes.
U.S. Pat. No. 5,896,474 (Van Deventer, et al.) describes a passive optical-connection network that has a protection configuration consisting of at least 2 sub-networks. Each of these sub-networks is comprised of an access node, a feed network, and a tree-shaped branched access network.
U.S. Pat. No. 6,226,111 (Chang, et al.) defines a cross-connect for a multi-ring, multi-channel telecommunications network, especially for a wavelength-division multiplexed (WDM) optical network. Each of the interconnected rings is self-healing because it has a redundant counter-rotating ring or excess capacity on pairs of counter-rotating rings.
U.S. Pat. No. 6,301,254 (Chan, et al.) illustrates a method and apparatus for the robust implementation and protection of Asynchronous Transfer Mode (ATM) traffic over a Synchronous Optical Network (SONET) unidirectional Path Switched Ring (UPSR). The traditional SONET bridging function is eliminated for the ATM traffic in favor of a selector function.
U.S. Pat. No. 6,414,765 (Li, et al.) describes a protection switch for use in a two-fiber optical channel shared protection ring. It includes an electrical switching circuit coupled to an optical signal monitor. The electrical switching circuit includes modular switching fabrics that respond to fault condition alarms provided by the optical signal monitor. Each modular switching fabric is versatile because it includes a ring switch mode that is responsive to the multi-wavelength channel failures, and a span switch mode that is responsive to the single wavelength channel failures.
U.S. Pat. No. 6,512,611 (Phelps, et al.) describes a method of deactivating protection fiber resources in an existing optical interconnected ring network or system. The invention uses 1:N protection principles to provide a single protection path on spans of interconnecting nodes common to two or more optical rings.
U.S. Patent Application 2003/0025956 (Li, et al.) provides a protection switch located at a node in a two-fiber optical channel protection ring. The protection switch includes a wavelength selective switch (WSS) coupled to the two-fiber optical channel protection ring. The WSS is configured to selectively drop at least one wavelength channel in the two-fiber optical channel protection ring. A dynamic spectral equalizer (DSE) is coupled to the two-fiber optical channel protection ring. The DSE is configured to substantially block wavelengths corresponding to at least one wavelength channel, and to optically manage at least one express wavelength channel not corresponding to the at least one wavelength channel.
U.S. Patent Application 2002/0080440 (Li, et al.) details a protection switch for use in a two-fiber optical channel shared protection ring. It includes an electrical switching circuit coupled to an optical signal monitor. The electrical switching circuit includes modular switching fabrics that respond to fault condition alarms provided by the optical signal monitor. Each modular switching fabric is versatile. It includes a ring switch mode that is responsive to the multi-wavelength channel failures and a span switch mode that is responsive to the single wavelength channel failures.